The present invention relates to a piston type variable displacement compressor.
Japanese Patent Laid-Open Publication No. 11-62824 and Japanese Patent Laid-Open Publication No. 2000-297746 describe examples of various displacement compressors. According to the technology described in Japanese Patent Laid-Open Publication No. 11-62824, a sleeve is fitted to a drive shaft to be slidable in the axial direction of the drive shaft. The sleeve is coupled to a swash plate. The sleeve moves axially along the drive shaft in accordance with the inclination angle of the swash plate. The drive shaft includes a gas passage which opens at the rear end of the drive shaft. The front end of the gas passage is connected to the interior of a crank chamber through a gas inlet passage extending through the drive shaft. The gas passage and the gas inlet passage form part of a bleed passage that connects the crank chamber to a suction chamber. The sleeve is designed to adjust the open amount of the gas inlet passage in accordance with the inclination angle of the swash plate. Specifically, the open amount of the gas inlet passage is adjusted to be maximal when the inclination angle of the swash plate is greatest and adjusted to be minimal when the inclination angle of the swash plate is smallest. Accordingly, the open amount of the gas inlet passage decreases as the inclination angle of the swash plate decreases when the displacement is decreased. This limits the amount of refrigerant gas that bleeds from the crank chamber towards the suction chamber through the gas inlet passage. As a result, the pressure of the crank chamber is increased.
According to the technology described in Japanese Patent Laid-Open Publication No. 2000-297746, a gas passage extending axially through a drive shaft. The front end of the gas passage is connected to an oil chamber by a first gas inlet passage extending through the front end of the drive shaft. The oil chamber is for collecting lubricating oil, which lubricates a front bearing and a lip seal. The front end of the gas passage is further connected to a crank chamber via the oil chamber. The rear end of the gas passage is directly connected to a rear region of the crank chamber by a second gas inlet passage extending through the rear end of the drive shaft. The rear end of the gas passage is further connected to a suction chamber. Thus, the gas passage forms part of a bleed passage. The drive shaft also supports a sleeve which moves along the drive shaft as it follows the inclination of a cam plate to open or close the second gas inlet passage according to the inclination angle of the cam plate. The sleeve closes the second gas inlet passage when the inclination angle of the cam plate relative to the drive shaft becomes minimal, that is, when the displacement is controlled to be minimal.
The interior of the compressor is lubricated with lubricating oil that circulates within the compressor together with refrigerant gas. There are cam plate-type compressors that use blow-by gas for positively supplying lubricating oil to a bearing, which supports the front end of a drive shaft, and to a seal device, which seals the space between the front end of the drive shaft and the compressor housing. The blow-by gas is discharged into a crank chamber from between a cylinder bore and a piston as the piston reciprocates. More specifically, the lubricating oil collected in the crank chamber is scattered in the crank chamber by the oscillation of the cam plate. The blow-by forces the scattered lubricating oil to the front of the crank chamber and positively supplies the lubrication oil to the bearing and a seal device. The amount of the blow-by gas increases as the piston stroke becomes longer, that is, as the displacement increases.
In the technology described in Japanese Patent Laid-Open Publication No. 11-62824, the amount of blow-by gas is minimal when the compressor displacement is minimal. Therefore, the lubricating oil supplied to the front bearing and the seal device by the blow-by gas will become insufficient, and the bearing and the seal device may not be sufficiently lubricated. As a result, in a clutchless compressor that substantially stops operating when the displacement is minimal, the durability of the compressor may be decreased.
In the technology described in Japanese Patent Publication No. 2000-297746, when the compressor displacement is minimal, the second gas inlet passage is closed when the first gas inlet passage is open. Thus, refrigerant gas mainly including blow-by gas is introduced into the gas passage through the first gas inlet passage. Therefore, even when the clutchless compressor stops operating, lubricating oil is positively supplied to the bearing and the seal device at the front end of the drive shaft by the refrigerant gas mainly including blow-by gas. This ensures the lubrication of the bearing and the seal device.
However, in the technology described in Japanese Patent Publication No. 2000-297746, the second gas inlet passage is not closed by the sleeve when the displacement of the compressor is controlled is significantly greater than the minimum state. Therefore, the refrigerant gas mainly including blow-by gas will bleed not only through the first gas inlet passage but also through the second gas inlet passage. Unless the amount of the refrigerant gas introduced into the gas passage through the first gas inlet passage is restricted, the amount of lubricating oil that is sent from the crank chamber to the suction chamber by the refrigerant gas will increase. This will increase the proportion of the lubricating oil in the refrigerant gas circulating through an external refrigerant circuit and decrease the heat exchange efficiency of an expansion device. As a result, the cooling capacity of an air conditioner will be decreased.